OVERVIEW: The overall goals of the research program have been to understand the molecular-genetic basis for hepatocarcinogenesis in hepadnavirus carrier. Hepadnaviral DNA integrations are agents of genetic change which can promote the process of hepatocarcinogenesis. Our recent data have established several features of the integration process. First, single and multiple integrations occur continuously through successive cell generations. Second, the integration frequency can vary dramatically in subclones of the same cell line. Third, integrations can be amplified and can also be lost from successive generations of cells. Fourth, the loss of an integration can be accompanied by the loss of cellular DNA associated with the integration. These results provide the basis for integrations to function as activators of protooncogenes, as well as agents of the loss of tumor suppressor genes during hepatocarcinogenesis. The specific aims of the current proposal will study the mechanisms responsible for the processes described above. SPECIFIC AIM 1: Studies on the molecular mechanisms associated with the acquisition and loss of DHBV integrations in LMH-D2 chicken hepatoma cells. SPECIFIC AIM 2: Studies on the effects of DHBV mutations which alter the structure of viral DNA's, or the amplification of nuclear CCC DHBV DNA's, on integrations in clonal populations of cells. SPECIFIC AIM 3: Studies on the effects of genotoxic agents, likely to be encountered during persistent infection, on the net accumulation or loss of DHBV integrations in LMH cells. SPECIFIC AIM 4: Studies on the acquisition, loss, or rearrangement of DHBV integrations during the growth of hepatomas in immunocompromized hosts. SPECIFIC AIM 5: Reconstitution of nu/nuupa mouse liver with woodchuck hepatocytes. Recent advances in the use of transgenic mice and hepatocyte transplantation now make it feasible for us to attempt to produce an animal model in which we will be able to clonally amplify and isolate woodchuck hepatocytes from all stages of carcinogenic progression.